An inventory control system for a digital signage network is provided that uses a denormalized relational database to maintain a record of each of a plurality of screen zones for displays of the network. An inventory column in the database may be used to track scheduling assignments for each day of a calendar year. A screen zone may be given a collective duration limit that prevents assignment of media content items to that screen zone if the assignment would cause the limit to be exceeded for any of the days in the scheduling request. A screen zone may also be designated as overbookable to allow a scheduling assignment even if the limit is exceeded, or may be designated as partially bookable to allow the assignment of media content items for only those days specified in the request for which the limit would not be exceeded.